Effective usage of energy is realized with the use of an electricity storage device such as a secondary battery. For example, in recent years, solar light power generation systems have been actively developed as eco-friendly, clean energy. Because a photoelectric conversion array which converts the solar light into electric power does not have an electricity storage function, the photoelectric conversion array is in some cases used in combination with a secondary battery. For example, the energy is effectively used by charge and discharge control to charge the electric power generated by the photoelectric conversion array into the secondary battery and to discharge the electricity from the secondary battery in response to a request from an external load or the like.
When an electricity storage system which executes the charge and discharge control in a combination of a secondary battery and a power supply is formed, a breaker is provided on the side of the electricity storage device, in order to protect the electricity storage device, which is the secondary battery.
Patent Literature 1 discloses a method of detecting, in a storage battery degradation state testing device of an alternating current uninterruptable power supply device which uses an inverter circuit receiving supply of electricity from a storage battery and a commercial power supply in combination, that a breaker provided between a charging circuit and the storage battery is not switched ON after the breaker is switched OFF when the storage battery is replaced, in which a storage battery voltage monitoring unit is provided, a capacitor is placed between the side of the charging circuit of the breaker and the ground, and detection of the reduction of the monitored voltage is facilitated.
As an electricity storage device protection technique different from the breaker, Patent Literature 2 discloses a charging method of a secondary battery wherein the secondary battery is rapidly charged while degradation of the battery performance is prevented by a pulse charge which repeats charging and discharging. In this reference, a switch and a discharging resistor are provided in parallel to the secondary battery, to form a discharging circuit.